menstrual cycle

• menstrual cycle

  • starts in early adolescence (around 12) and controlled by hormones
  • average cycle is 28 days
  • ovulation (release of an egg) occurs about halfway through the cycle (day 14) and the egg travels down the oviduct to the uterus
  • failure to fertilise the egg causes menstruation - caused bvy the breakdown of the thickened lining of the uterus
  • menstruation lasts around 5-7 days and the lining starts to thicken again in preparation for possible implantation in the next cycle
• Changes in the lining of the uterus during the menstrual cycle

  A) menstruation

  B) builds up

  C) maintained

  D) cycle

  E) breaks

  F) down

  G) menstruation

  
• oestrogen and progesterone

  • menstrual cycle is controlled by hormones released from the ovary and the pituitary gland in the brain
  • oestrogen levels rise rom day 1 to peak just before day 14
  • this causes the uterine walls to start thickening and the egg to mature
  • progesterone stays low from day 1 - 14 and starts to rise since ovulation has occurred
  • the increasing levels cause the uterine linings to thicken further; a fall causes it to break down (menstruation)
• label

  A) oestrogen

  B) ovulation

  C) progesterone

  D) 7

  E) 14

  F) 28

  
• OESTROGEN

  • stimulates growth and repair of uterus lining (to replace lining lost during menstruation)
  • post ovulation, inhibits FSH and stimulates LH production in the pituitary gland
• PROGESTERONE

  • maintains and thickens lining of uterus
  • inhibits FSH and LH production
  • if fertilisation doesn't occur, levels drop and menstruation occurs
• FSH and LH

  • FSH (follicle stimulating hormone) is released by the pituitary gland and causes an egg to start maturing in the ovary
  • also stimulates the ovaries to start releasing oestrogen
  • the pituitary gland is stimulated to release LH (luteinising hormone) when oestrogen levels have reached their peak
  • LH causes ovulation to occur and also stimulates ovaries to produce progesterone
• interaction between all 4 hormones pt 1

  1. the pituitary gland produces FSH which stimulates the development of a follicle in the ovary
  2. an egg develops inside the follicle and the follicle produces oestrogen which causes growth and repair of the uterus wall lining and inhibits production of FSH
  3. when oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (day 14)
  4. the follicle becomes the corpus luteum and starts producing progesterone which maintains uterus lining (thickness of wall)
• interaction between all 4 hormones pt 2

  1. if ovum not fertilised, the corpus luteum breaks down and progesterone levels drop

  • this causes menstruation, where the uterus lining breaks down and is removed through the vagina


  2. if pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy

  • it does this until the placenta has developed, at which point it starts secreting progesterone throughout the pregnancy
• label

  A) pituitary gland

  B) FSH

  C) LH

  D) oestrogen

  E) progesterone

  F) ovaries

  G) inhibits

  H) blood

  I) ovary

  J) oestrogen

  K) progesterone

  L) egg

  M) maturation

  N) ovulation

  O) uterus

  P) oestrogen

  Q) progesterone

  R) development

  S) maintenance

  T) lining

  
• If the egg becomes fertilized, progesterone continues to be secreted, first by the corpus luteum and then by the placenta, until the child is born. Progesterone blocks the release of more hormones from the pituitary gland, so that further ovulation does not normally occur during pregnancy.
• 1-7: FSH from pituitary gland stimulates maturation of egg follicles -> stimulates oestrogen production -> stimulates growth & repair of lining + secretion of LH from pituitary gland

  8-14: release more oestrogen = more LH. progesterone released before ovulation. a surge of LH stimulates the mature follicle to break open, triggering ovulation around day 14. egg released. the follicle empty of its egg is the corpus luteum

  15-21: corpus luteum secretes progesterone which maintains lining of uterus and inhibits secretion of FSH & LH, preventing growth / development of more follicles
• 22-28:

  if not fertilised

  • oestrogen & progesterone levels drop -> lining breaks down -> menstruation
  • low progesterone allows increase in secretion of FSH from pituitary gland -> start of next cycle

  if fertilised

  • progesterone levels remain high, maintaining thickness of lining in preparation for pregnancy
  • inhibits FSH secretion, preventing further growth and development of follicles